Information recording systems and methods utilizing controlled mark-length

ABSTRACT

The mark-length recording system whereby information is recorded by changing the lengths of a recorded portion and an unrecorded or erased portion has a problem that, when new information is recorded in an already recorded region, the newly recorded information may deteriorate in reliability because the length and width of the newly recorded mark are different from those of the previously recorded mark and a part may exist that is not completely erased at the time of overwriting. The invention widens a setting freedom of the recording power and controls the length and width of the recorded mark by making the effective recording pulse length (the length from a rise of a first pulse to a fall of a last pulse) satisfy a relation: (effective recording pulse length)&lt;(recording code length, i.e., the length of data to be recorded)−2T(twice the reference clock cycle).

FIELD OF THE INVENTION

The present invention relates to an information recording andreproducing apparatus for recording and reproducing information on aninformation recording medium, and more specifically to an informationrecording method for recording information by a mark-length recordingsystem with the use of laser light, and an information recordingapparatus for such an information recording method.

BACKGROUND OF THE INVENTION

A technology of recording and reproducing information on/from theinformation recording medium using laser light has already achieved apractical use of an optical disk apparatus etc. As one method for arewritable optical disk apparatus, there is a phase change type opticaldisk that utilizes a reversible phase change between crystalline andamorphous states. In order to obtain these two states, light of a highpower (recording power) is irradiated on the recording medium, which isheated over a melting point and then is quenched quickly to convert tothe amorphous state; light of an intermediate power (erasing power)lying between the above-mentioned high power and a reproducing power isirradiated on the recording medium, which is heated up to thecrystallizing temperature and is cooled gradually to convert to acrystalline state. Therefore, overwriting can be performed with light ofa single laser.

Conventionally, in the recording method based on the above-mentionedlight irradiating method, as described in U.S. Pat. No. 5,490,126, U.S.Pat. No. 5,636,194, and the DVD-RAM JIS Standard (120 mm DVD RewritableDisk JIS X 6243/P86, Attachment H, Definition of Writing Pulse), atleast three power levels consisting of the recording power (high powerlevel) for overwriting, the erasing power (medium power level), and thereproducing power for reducing thermal interference (low power level)are used; and the recording mark is classified into three kinds, namelya first part, an intermediate part, and a last part, and, an informationis recorded by a recording pulse whose effective length (length from arise of the first pulse to a fall of the last pulse) corresponds to thelength of data to be recorded (recording code length). Further, thisrecording method adopts a recording method where, in the first part andin the last part, light of the above-mentioned recording power isirradiated for a constant period of time; in the intermediate part,light of the recording power and light of a power smaller than therecording power (erasing power) are switched alternately and irradiatedso that the cycle thus created becomes smaller than the above-mentionedconstant period of time; and after the light of the recording powerirradiated in the last part, light of a power (reproducing power) lowerthan the erasing power is irradiated for a constant period of time todecrease the thermal interference.

SUMMARY OF THE INVENTION

In order to increase storage capacity in the next-generation opticaldisk, it is preferable that the size of a record mark is smaller thanthat of the present optical disk (for example, DVD-RAM Version 1.0/2.0).However, if the mark whose recording code length is of the order of 0.15to 0.20 μm is intended to be recorded by a recording method forrecording the mark whose recording code length is of the order of 0.42to 0.615 μm (DVD-RAM Version 1.0/2.0), a mark of a length of the orderof 0.21 to 0.28 μm is formed even using an apparatus that features alaser wavelength=0.405 μm and an NA=0.85. That is, there was a problemthat a mark about 1.4-times larger than the targeted recording codelength is formed. Further, even when the recording is performed usingthe above-mentioned recording method with reduced laser output, it isdifficult to avoid the problem that a mark whose length is 1.4-timeslarger than the recording code length of the targeted mark is formed.Moreover, if the recording is performed with a laser output that canmake the mark agree with the recording code length, there is a problemthat a sufficient mark width cannot be obtained, which causes decreasein the signal amplitude at the time of reproducing and hence reduce inthe signal-to-noise ratio, and consequently the reliability of theinformation is impaired and the like.

It is the object of the present invention to provide an informationrecording method whereby a recording operation of recordable opticaldisk (e.g., DVD-R) or rewritable optical disks (i.e., DVD-RAM andDVD-RW), in both of which the information is recorded with a recordingcode length shorter than that of the current optical disk, is controlledappropriately and also an information recording apparatus for such aninformation recording method.

In order to attain the above-mentioned object, the recording methodaccording to one aspect of the present invention is a method forrecording data on an optical disk by irradiating laser light on theoptical disk and forming a mark whose length is an integral multiple ofthe reference clock length, characterized in that, as irradiationpowers, the above-mentioned laser can irradiate the optical disk at anyone of four laser powers that satisfy a relation:

ti first power>second power>third power>fourth power,

and a sum of the lengths of a pulse of the above-mentioned first powerand of a pulse of the above-mentioned fourth power at the time offorming the mark is made to be shorter than the length of the mark minustwice the reference clock length.

Further, the recording method according to another aspect of the presentinvention is a method for recording the data on an optical disk byirradiating laser light on the optical disk and forming a mark whoselength is an integral multiple of the reference clock length,characterized in that, as irradiation powers, the above-mentioned lasercan irradiate the optical disk at any one of four laser powers thatsatisfy a relation:first power>second power>third power>fourth power,and the length of a first pulse of the first power at the time offorming the mark is made to be shorter than twice the length of a pulseof the fourth power that follows the first light of the first power.

Moreover, the recording method according to still another aspect of thepresent invention is a method for recording the data on an optical diskby irradiating laser on the optical disk and forming a mark whose lengthis an integral multiple of the reference clock length, characterized inthat, as irradiation powers, the above-mentioned laser can irradiate theoptical disk at any one of four laser powers that satisfy a relation:first power>second power>third power>fourth power,and the length of a first pulse of the fourth power at the time offorming the mark is made to be longer than the length of a pulse of thefourth power that follows the first pulse of the fourth power.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an information recording apparatus in oneembodiment according to the present invention.

FIG. 2 is a waveform chart for explaining the recording method in theone embodiment according to the present invention.

FIG. 3 is a recording waveform chart in the one embodiment according tothe present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows the block diagram of the one embodiment of the informationrecording apparatus that implements the recording method according tothe present invention. In the block diagram, the numeral 1 is a laser,the numeral 2 is an APC (Auto Power Control) circuit, the numeral 3 is ahigh-frequency superimposing circuit, the numeral 4 is a current sourcefor reproducing, the numeral 5 is a first recording current source, thenumeral 6 is a second recording current source, the numeral 7 is a thirdrecording current source, the numeral 8 is a fourth recording currentsource, the numeral 9 is a first switch, the numeral 10 is a secondswitch, the numeral 11 is a third switch, the numeral 12 is a fourthswitch, the numeral 14 is a counter, the numeral 15 is a memory, thenumeral 13 is a recording pulse generating circuit composed of thecounter 14 and the memory 15, the numeral 16 is a reference clock, thenumeral 17 is a sequence of recording codes, the numeral 18 is a firstrecording pulse, the numeral 19 is a second recording pulse, the numeral20 is a third recording pulse, and the numeral 21 is a fourth recordpulse.

At the time of reproducing, the laser 1 is oscillated at a reproducingpower level Pr by the APC circuit 2. The high-frequency superimposingcircuit 3 is provided to reduce laser noise arising from the laser 1,but the high-frequency superimposition may be stopped at the time ofrecording/erasing from the viewpoint of a laser life. At the time ofrecording, the switches 9-12 for controlling the currents from therecording current sources 5-8 are controlled by four kinds of recordingpulses 18-21, which enables the laser 1 to emit the laser powernecessary for recording the information. The memory 15 storescombinations of recording pulses (hereinafter referred to as therecording pulse trains) used to form nine kinds of marks of 3T (channelbits) to 11T, which are necessary in the mark-length recording system,and outputs a recording pulse train in response to an input from thecounter 14. The reference clock 16 and the sequence of recording codes17 that is information to be recorded are inputted into the counter 14,where the sequence of recording codes 17 is decomposed into marks(recorded portions) and spaces (erased portions) to be recorded insynchronization with the reference clock 16, the recording code lengthis counted, and consequently the memory 15 outputs a recording pulsetrain that corresponds to the recording code length.

An outline of the combination of the control signal and the recordingwaveform length at the time of recording 3T and 6T marks on the opticaldisk, where the information is recorded with a recording code lengthshorter than that of the current optical disk, will be describedreferring to FIG. 2. FIG. 2(A) and FIG. 2(B) show the reference clock 16and the sequence of recording codes 17, respectively, which are inputtedinto the counter 14. The counter 14 decomposes the sequence of recordingcodes 17 into the recorded (mark) portions (H level) and erased (space)portions (L level) at positions of the rise or fall of the referenceclock 16, and counts the recording code length; and then, the memory 15outputs a recording pulse train corresponding to the recording codelength. FIG. 2(C) shows the recording pulse outputted from the memory15, and FIG. 2(D) shows a laser power emitted from the laser 1 to theoptical disk.

Here, the first recording pulse 18 has a power level of Pw (recordingpower level), the second record pulse 19 has a power level of Pe(erasing power level), the third recording pulse 20 has a power level ofPb, and the fourth recording pulse 21 has a power level of Pc. At thetime of recording 3T and 6T marks, the high-frequency superimposingcircuit 3 is stopped, a power level Pr′ that is maintained by the APCcircuit 2 is used as a base power, on which the power levels (Pw, Pe,Pc, Pb) are superimposed. Here Pr′ is a power level when thehigh-frequency superimposition circuit is stopped, and this power levelis lower than the reproducing power level Pr. Further, for the spaceportions, the power level of Pe is superimposed on the power level ofPr′ and is irradiated on the optical disk.

In the intermediate part of a portion where the 3T mark is to be formed(when the second recording pulse is off), the light at the power levelof Pw heats up the recording medium, and the light at the power level ofPc suppresses the thermal interference and also controls shapes of frontand rear ends of the mark that is being formed on the recording medium.Further, in the intermediate part of a portion where the 6T mark is tobe formed, the light at the power levels of Pw, Pb, and Pc controls theshapes of front and rear ends of the mark that is being formed on therecording medium. That is, at the time of recording 3T and 6T marks, thelaser light is irradiated on the recording medium at the laser powersshown in FIG. 2(D).

The details of the control signal and the recording waveform length atthe time of the recording of the optical disk on which the informationis recorded with a recording code length shorter than that of thecurrent optical disk will be described referring to FIG. 3. The 8/16modulation is one whereby information is recorded using marks and spacesof 3T to 11T. Although the laser powers corresponding to the recordingcodes of 3T to 5T are made to vary intricately as shown in the figure,the laser powers for the recording codes of 6T to 11T are such that apulse train (T_(MP), T_(MC)) synchronized with the reference clock 16 isadded to the recording code 5T by the difference number of cyclesbetween the recording code 5T and a recording code in question. Here,the laser is driven alternately at two power levels of Pw and Pb. Thereason why similar waveforms are used for 6T and thereafter is that thesize (the length) of the mark that is formed depends on outflow of theheat in the recording medium, the size of the irradiated light spot, andthe length of the mark to be formed. Hereafter, the effective recordingpulse length for each recording code etc. will be described concretelyreferring to FIG. 3(C).

First, in order to form the recording code 3T, the light is irradiatedat the recording power Pw for a first pulse length T_(FP)=0.563T. Theeffective recording pulse length consists of the first pulse lengthT_(FP), and needs to be shortened from the recording code length by theamount: (recording code length 3T)−T_(FP)=2.437T as a control in thetime-axis direction.

For the recording code 4T, the effective recording pulse length becomes1.688T that is a sum of the lengths of three kinds of pulses: a firstpulse length T_(FP)=0.625T, a first cooling pulse length T_(FC)=0.5T,and a last pulse length T_(LP)=0.563T, and it needs to be shortened fromthe recording code length by the amount: (recording code length4T)−(effective recording pulse length)=2.312T as a control in thetime-axis direction. Further, the ratio of the first pulse length to thefirst cooling pulse length (T_(FP)/T_(FC)) is 1.25.

The effective recording pulse length for the recording code 5T is 2.315Twhich is a similar recording waveform as the recording code 4T. Also inthis case, as with the recording code 4T, the effective recording pulselength needs to be shortened from the recording code length by 2.685T asa control in the time-axis direction. Further, a ratio of the firstpulse length to the first cooling pulse length (T_(FP)/T_(FC)) isapproximately 1.25.

For the recording code 6T, the effective recording pulse length becomes3.315T that is a sum of the lengths of five kinds of pulses: a firstpulse length T_(FP)=0.94T, a first cooling pulse length T_(FC)=0.75T, anintermediate pulse length T_(MP)=0.375T, an intermediate cooling pulselength T_(MC)=0.625T, and a last pulse length T_(LP)=0.625T, and itneeds to be shortened from the recording code length by the amount:(recording code length 6T)−effective recording pulse length)=2.685T as acontrol in the time-axis direction. Further, the ratio of the firstpulse length to the first cooling pulse length (T_(FP)/T_(FC)) isapproximately 1.25 as with the case of the recording code 5T. Moreover,the ratio of the first cooling pulse length to the intermediate coolingpulse length (T_(FC)/T_(MC)) is 1.2.

For the recording codes 7T to 11T, the recording waveforms are ones thata combination of the intermediate pulse length T_(MP)=0.375T and theintermediate cooling pulse length T_(MC)=0.625T is added to theintermediate part of the recording waveform for the recording code 6T,one by one, respectively.

By performing such recording waveform control as explained in theforgoing, a heat storage effect can be kept constant and the width ofthe mark can be controlled constant regardless of the length of arecording code. This control is extremely effective for the mark-lengthrecording system where a mark smaller than a light spot size that isdefined by λ/NA is used as a shortest mark. Further, also in thehindmost part of the mark, both a shape of the rear end of the markformed in the recording medium and the thermal interference can becontrolled by the fourth recording pulse 21, so that a mark whoserecording code length is of the order of 0.15 to 0.20 μm can be recordedadequately.

Note that, although this embodiment adopts a configuration in whichrecording pulse trains corresponding to the nine kinds of recording codelengths of 3T to 11T are stored, the embodiment may adopt aconfiguration in which a recording pulse train corresponding to arecording code length of 2T is stored additionally according to therecording medium and the recording apparatus. Moreover, in thisembodiment, the differences between the recording code lengths and theeffective recording pulse lengths are set to 2.315T to 2.685T, but evenif this difference is set to 2T or so, a similar effect can be obtained.Furthermore, the ratio of the first pulse length to the first coolingpulse length (T_(FP)/T_(FC)) is set to approximately 1.25, but even ifthis ratio is set to 2 or so, a similar effect can be obtained.

According to the present invention, in the mark-length recording systemwhere a mark smaller than a light spot size that is defined by λ/NA isused as a shortest mark, there can be offered the effect that the lengthand width of the record mark are controlled in a highly accurate mannerregardless of variation in lengths of the record marks and spaces, whichenables the information to be recorded densely, and the effect that thereliability of the information is improved.

1. An information recording method for recording information based on amark-length recording system where laser light irradiates an informationrecording medium, an information-recorded portion being physicallydifferent from an information-unrecorded portion formed in a recordingarea on the information recording medium, and the information-recordedportion and one of the information-unrecorded portion or an erasedportion are changed in length, and that performs recording, reproducing,and erasing of information on the information recording medium, themethod comprising: a step of using a recording waveform for forming arecord mark, which recording waveform is substantially composed of threepulses: a first pulse, an intermediate pulse, and a last pulse; and astep of controlling the recording waveform to satisfy: a relationship inwhich the length of the first pulse is less than two times as long asthe length of a first cooling pulse; a sum of the length of theintermediate pulse and the length of an intermediate cooling pulse is1T; and the intermediate pulse and the intermediate cooling pulse aresequentially added to an intermediate portion of the recording waveformof a recording code 6T, when the length of the recording code is morethan 6T, where T is a reference clock period; wherein the recording isperformed by using laser light having a wavelength of about 0.4 μm andproduced by an apparatus having an NA of about 0.85, and wherein whenthe length of the recording code is greater than 6T, the ratio of aintermediate pulse length to a first cooling pulse length is less than1.0 and the ratio of the intermediate pulse length to an intermediatecooling pulse length is less than 1.0.
 2. The information recordingmethod according to claim 1, wherein the recording waveform iscontrolled so that a pulse train formed by the intermediate pulse andthe intermediate cooling pulse are added to the intermediate portion ofthe recording waveform of the recording code 6T.
 3. An informationrecording method for recording information based on a mark-lengthrecording system where laser light irradiates an information recordingmedium, an information-recorded portion being physically different froman information-unrecorded portion, and the information-recorded portionand one of the information-unrecorded portion and an erased portion arechanged in length, and that performs recording, reproducing, and erasingof information on the information recording medium, the informationrecording method comprising: a step of using a recording waveform usedfor forming a record mark which is substantially composed of threepulses: a first pulse, an intermediate pulse, and a last pulse; a stepof controlling the recording waveform to satisfy a relationship in whichthe length of a first cooling pulse is greater than the length of anintermediate cooling pulse; and a step of controlling the waveform sothat a sum of the length of the intermediate pulse and the length of theintermediate cooling pulse is 1T, and the intermediate pulse and theintermediate cooling pulse are sequentially added to an inter mediateportion of the recording waveform of a recording code 6T when the lengthof the recording code is more than 6T, where T is a reference clockperiod; wherein the recording is performed by using laser light having awavelength of about 0.4 μm and produced by an apparatus having an NA is0.85, and wherein when the length of the recording code is greater than6T, the ratio of an intermediate pulse length to a first cooling pulselength is less than 1.0 and the ratio of the intermediate pulse lengthto an intermediate cooling pulse length is less than 1.0.
 4. Theinformation recording method according to claim 3, wherein the recordingwaveform is controlled so that a pulse train formed by the intermediatepulse and the intermediate cooling pulse are added to the intermediateportion of the recording waveform of the recording code 6T.
 5. Aninformation recording apparatus which records information based on amark-length recording system where laser light irradiates an informationrecording medium, a recorded portion being physically different from aninformation-unrecorded portion, and the recorded portion and one of theinformation-unrecorded portion and an erased portion are changed inlength, whereby the information is recorded, and that performsrecording, reproducing, and erasing of information on the informationrecording medium the information recording apparatus comprising: a laserlight source to produce laser light for irradiation on the informationrecording medium; and a controller which controls a recording waveformused for forming a record mark which is substantially composed of threepulses: a first pulse, an intermediate pulse, and a last pulse, and therecording waveform is controlled so as to satisfy a relationship inwhich the length of the first pulse is less than two times as long asthe length of a first cooling pulse, and is controlled so that a sum ofthe length of the intermediate pulse and the length of an intermediatecooling pulse is 1T and the intermediate pulse and the intermediatecooling pulse are sequentially added to an inter mediate portion of therecording waveform of a recording code 6T when the length of therecording code is more than 6T, where T is a reference clock period;wherein the recording is performed by using laser light having awavelength of about 0.4 μm and produced by an apparatus having an NA ofabout 0.85, and wherein when the length of the recording code is greaterthan 6T, the ratio of an intermediate pulse length to a first coolingpulse length is less than 1.0 and the ratio of the intermediate pulselength to an intermediate cooling pulse length is less than 1.0.
 6. Theinformation recording apparatus according to claim 5, wherein therecording waveform is controlled so that a pulse train formed by theintermediate pulse and the intermediate cooling pulse are added to theintermediate portion of the recording waveform of the recording code 6T.7. An information recording apparatus which records information that isbased on a mark-length recording system where laser light irradiates aninformation recording medium, a recorded portion being physicallydifferent from an information-unrecorded portion is formed in arecording area on the information recording medium, and the recordedportion and one of the information-unrecorded portion or an erasedportion are changed in length, and that performs recording, reproducing,and erasing of information on the information recording medium orperforms direct recording of different information in an alreadyrecorded region in an overwriting manner, wherein the informationrecording apparatus comprises: a laser light source to produce laserlight for irradiation on the information recording medium; and acontroller which controls a recording waveform used for forming a recordmark which is substantially composed of three pulses: a first pulse, anintermediate pulse, and a last pulse, and the recording waveform iscontrolled so as to satisfy a relationship in which the length of afirst cooling pulse is greater than the length of an intermediatecooling pulse, and is controlled so that a sum of the length of theintermediate pulse and the length of the intermediate cooling pulse is1T, and the intermediate pulse and the intermediate cooling pulse aresequentially added to an intermediate portion of the recording waveformof a recording code 6T when the length of the recording code is morethan 6T, where T is a reference clock period, and the informationrecording apparatus performs information recording by using thecontrolled recording waveform, wherein the recording is performed byusing laser light having a wavelength of about 0.4, um and produced byan apparatus having an NA of about 0.85, and wherein when the length ofthe recording code is greater than 6T, the ratio of an intermediatepulse length to a first cooling pulse length is less than 1.0 and theratio of the intermediate pulse length to an intermediate cooling pulselength is less than 1.0.
 8. The information recording apparatusaccording to claim 7, wherein the recording waveform is controlled sothat a pulse train formed by the intermediate pulse and the intermediatecooling pulse are added to the intermediate portion of the recordingwaveform of the recording code 6T.